OSMOSIS

Hypotonic solution

If the medium sorrounding the cell has a higher concentration than the cell ,i.e., if the solution is a very dilute solution, the cell will gain water by osmosis. Such a dilute solution is called hypotonic solution.

Isotonic solutionif the medium sorrounding the cell is exactly the same water concentration as the cell, there will be no net movement of water across the plasma membrane. Such a solution is called isotonic solutiuon.

Hypertonic sloutin

If the medium has a lower concentration of water than mthe cell, i.e. ,if it is very

concentrated solution the cell will lose water by osmosis.

Such a concentrated solutions called hypertonic solution

Activityosmosis with egg

a. Take hen’s egg and remove the egg shell by putting the egg in dilute hydrochloric acid[HCl]. The shell of the egg is made up mainly of calcium bicarbonate. A thick outer skin [called shell membrane ],encloses the egg. Put this processed egg in pure water and observer for 3-5 minutes. What do you observe?

Activityosmosis with egg

You will observe that the egg swells

because water enter the egg by osmosis

Activityosmosis with egg

b. Place a similar de-shelled egg in a concentrated salt solution and observe for 5 minutes. The egg shrinks, why??

Activityosmosis with egg

The egg shrinks since water passes out of the egg solution into the salt solution because the salt solution is more concentrated

Activityosmosis with dried raisins

and apricots

Put dried raisins or apricots in plain water and leave them for some time. Then place them into a concentrated solution of sugar or salt. You will observe the following:

Activityosmosis with dried raisins

and apricotsa. Each gains water and

swells when placed in water.

b. However , when placed in water in the concentrated solution it loses water and consequently shrinks.

Examples of osmosis

Unicellular freshwater organisms and most plant cells tend to gain water through osmosis absorption of water by plant roots is also an example of osmosis.